About 10.4 percent of the world's land surface, or approximately 6,020,000 square miles (15,600,000 square kilometers), is glaciated. Glaciated means permanently covered with ice. That ice takes the form of glaciers, ice sheets, or ice caps.

A glacier is a large mass of land ice that flows, under the force of gravity, at a rate of 10 to 1,000 feet (3 to 300 meters) per year. Glaciers on steep slopes may flow faster. For example, the Quarayoq Glacier in Greenland moves an average of 65 to 80 feet (20 to 24 meters) per day.

An ice sheet is a thick glacier that's larger than 19,000 square miles (50,000 square kilometers). An ice sheet blankets an area of land, completely covering its mountains and valleys, flowing outward in all directions. An ice cap is a sheet of ice and snow that continuously covers an area of land, but is smaller than an ice sheet.